This invention relates to fuel preparation systems for internal combustion engines and is particularly concerned with an arrangement which improves the performance of a fuel injection system at low engine speeds and light load conditions.
Fuel preparation systems for internal combustion engines such as used in automobiles require that the throttle provide control over a very substantial range of induction flows encompassing the full range of engine operating speeds and loads. In today's internal combustion automotive engines, the problem is compounded because Federal regulations mandate a minimum amount of exhaust emission pollutants and hence control of the mixture preparation is extremely important if compliance with these regulations is to be achieved. While it is important to provide accurate control over the full operating range of the engine, such control becomes particularly critical when the engine is operating at idle and low engine speeds and at light loads. This is because if the proper fuel/air mixture is not available to the cylinders of the engine under such operating conditions, the engine can stumble or even stall.
In a conventional carburetor there are typically two metering systems, namely a main metering system and an idle metering system. The main metering system usually involves a venturi located upstream of the throttle blade at which fuel is introduced into the induction air stream when the engine is operating at speeds above idle and at more than the minimum engine load.
The idle system on the other hand has an idle port located downstream of the throttle blade whereby fuel mixed with air is introduced into the induction air below the throttle blade. The idle port has an adjusting screw allowing mixture settings for best engine idle operation. There is a transfer slot in the wall of the throttle bore just upstream of the idle port which, when the throttle blade is in the idle position, serves to conduct part of the induction air around the throttle blade so that it can be inducted along with part of the idle fuel into the combustion chambers of the engine plus the adjustable idle fuel mixed with air from the idle port.
The advent of electronics in internal combustion engine controls has created the possibility of more precise control of air/fuel ratios toward the objective of minimizing exhaust pollutions. This means that electronic control of fuel injectors can provide very precise metering of fuel into the induction passage of an engine. However, the fact that the amount of fuel metered into the induction passage can be accurately controlled by the use of electronics is not in and of itself a guarantee that a suitable air/fuel mixture preparation will occur.
In the development of throttle body injection systems wherein a fuel injector is mounted on a throttle body in the vicinity of the throttle blade, a problem has been observed which may have heretofore escaped detection. Particularly, the problem is that when fuel is sprayed from the injector onto the walls of the induction bore and onto the throttle blade disposed in said bore, a mixture restriction occurs at low engine speeds and light engine loads (high vacuum conditions) which prevents the attainment of a sonic mixture velocity. This adversely affects the quality of the mixture preparation and it means that at very low idle speeds the engine may begin to run rough and even so far as to stall out even though the appropriate amount of fuel is being injected. In the carburetor, of course, this problem does not occur because of the fact that the idle port is disposed downstream of the closed throttle blade where there is a high vacuum sucking fuel in. In a throttle body type injection system the inclusion of a separate idle metering system analogous to that of the carburetor would tend to defeat the whole purpose of using electronically controlled injectors because the precise control which electronics can provide would be lost when the engine is idling or running at very light loads. However, to provide the proper restriction at low idle speeds it is necessary that the throttle blade be able to fully or almost close to its full closed position. The problem is also compounded with single bore throttle bodies because of the divergent requirements at wide open throttle (WOT) vis-a-vis idle. For minimum restriction at WOT the induction bore should have as large a diameter as possible; yet the larger the bore, the more difficult it is to achieve proper idle fuel/air mixture preparation.
The present invention arises through the recognition of the foregoing problem and provides a solution to it whereby in a throttle body fuel injection system, fuel is introduced into the induction passage by the injector exclusively upstream of the throttle blade over the full operating speed and load range of the engine including engine idle at minimum load, and aperture means are provided which are effective, with the throttle blade at and adjacent its closed position, to establish communication between points upstream and downstream of the induction passage relative to the throttle blade and are of sufficient size to conduct both the induction air and the entrained fuel as a mixture at sonic velocity past the throttle blade sufficient to keep the engine running even at low speeds and minimum load. One advantage is that low idle speeds can be obtained while still complying with pertinent regulations. This means improved fuel economy and less wear and tear on the engine.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered with the accompanying drawings.
The drawings disclose preferred embodiments of the invention in accordance with the best mode presently contemplated for carrying out the invention.